A review of multifunctional optical gap-surface plasmon metasurfaces

—Gap-surface plasmon (GSP) metasurfaces that consist of metallic resonators, a middle dielectric spacer, and a back metallic reflector have become an emerging research area due to their excellent properties, such as ease of fabrication, high efficiency, and unprecedented capabilities of controlling reflected fields. In this concise review, we introduce our efforts in exploring the physical principles and fascinating applications of multifunctional GSP metasurfaces in the optical range. Starting with a typical GSP meta-atom, we present the concept and mechanism of simultaneous and independent phase and polarization control. We then overview some typical applications of GSP metasurfaces, including beam-steering, surface plasmon polariton coupling, metalenses, meta-waveplates, and dynamical metasurfaces. The review is ended with a short perspective on future developments in this area.